Common exercise machines work specific muscle groups by resisting motion in a single degree of freedom, generalized direction. Typically, power is transmitted cyclically over the range of joint motion from the user's muscles, to the skeleton, through the machine interface and mechanical linkage, to the resistance mechanism. The resistance mechanism may be a guided weight, spring, friction belt, hydraulic cylinder or the like.
Biomechanical factors, such as force-length and force-velocity properties of muscle (Zajac 1989), muscle moment arms, and skeletal geometry, influence the capacity of the user to produce force in the generalized direction. These factors result in a generalized strength for the user on a particular machine which varies with both position and velocity over the range of exercise motion. Similarly, the resistance response of the machine may vary with position and velocity due to the mechanical advantage (MA) of the linkage and the properties of the resistance mechanism.
Typical prior art flexion and extension machines such as those used for elbows are illustrated in FIGS. 1A through 1C. They include a drive arm moveable with respect to a frame, the frame typically including upright. The drive arm is pivotally connected to the frame and, the removed end will engage the user's wrist or hand area, which will activate and pivot the drive arm. Since the drive arm is attached to a resistance mechanism, such as weights, springs or a hydraulic cylinder (as shown in FIGS. 1-3), the user must overcome the resistance.
Prior art machines link, for example, a hydraulic cylinder, a fixed point on the cylinder body pivotally to the frame and a point on the removed end of the rod of the hydraulic cylinder to the drive arm. This gives the benefit of balancing user strength and machine resistance by providing variable resistance. Some other existing exercise equipment, such as a Nautilus, employs cables, cams and weight to provide an appropriate variable resistance. In the prior art, “2-bar linkage designs” as set forth in FIGS. 1A and 1B (the two bars being the upright and the pivoting drive arm), at flexion angles between about 0 and 60 degrees (flexion angle measured between the user's upper arm and lower arm), the mechanical advantage of the system increases, then from 60 degrees to about 120 degrees the MA decreases. Thus, variable resistance is achieved.
This “low-high-low” mechanical advantage change as the flexion angle changes between about zero and about 120 degrees tends to balance the generalized strength of the typical user, who is weaker at the lower angles, stronger around 60-80 degrees and then weaker again at high flexion angles greater than about 60-80 degrees. Thus, the variable resistance machine such as the 2-bar design illustrated in FIG. 1A through 1C tends to provide greatest resistance when generalized muscle strength is greatest (60-80 degrees) and less resistance (through lower mechanical advantage) where muscle strength is weaker.
However, Applicant provides a novel linkage that yields better balance in a variable resistance 4-bar pivoting drive arm exercise machine in order to optimize exercise benefits.
Applicant achieves these results in a novel 4-bar flexion and extension machine which typically comprises a hydraulic cylinder having a movable plunger or piston and a hydraulic cylinder body. The hydraulic cylinder body is pivotally attached to a stationary frame or an upright. Also attached to the upright is a pivoting drive arm, actuated by the exerciser machine user. The removed end of the plunger is located, by links, pivotally, to both the stationary frame or upright and the pivoting drive arm.
The result is an improved exercise machine that better balances the variable resistance provided by the machine to the typical general muscle strength variation of user so as to achieve balance and smoothness of movement and consistency of velocity over the desired range of motion.